Train-to-wayside communication system using trackside conductors

ABSTRACT

A track communication system for moving trains, has an open wire transmission line extending along the track comprising two insulated conductors, the characteristic impedance of the transmission line being maintained substantially constant by the presence of a sectionalized conductor adjacent one of the insulated conductors each section of which is short circuited to a conductor adjacent the other insulated conductor of the transmission line. In an alternative embodiment, one insulated conductor of the transmission line is replaced by a rail of the track to which each section of the sectionalized conductor is short circuited.

United States Patent 11113,585,505

[72] Inventor Harry Ileggie Ogilvy I561 References Cited Birmingham,England UNITED STATES PATENTS [21] P 2.150.857 3/1939 Edwards 340/48 x[221 Filed 15, 1968 3,466,551 9/1969 Bigelowv. 325/51 ux [45] 1971 3 470474 9/1969 Rohrer 325/28 x [73] Assignee British Railways Board L d E ld Pnmarv Examiner-Robert L. Griffin [32] Priority Jan. 15, 1968Assistant ExaminerR, S. Bell 3 3] Great B i i AttorneySommers & Young[31] 202l68 [54] TRAIN-TO-WAYSIDE COMMUNICATION SYSTEM USING TRACKSIDECONDUCTORS 2 Claims, 7 Drawing Figs.

179/82, 325/28, 340/47 [51] lnt.Cl H04b 13/00 [50] Field of Search325/28, 29,

TRAIN-TO-WAYSIDE COMMUNICATION SYSTEM USING TRACKSIDE CONDUCTORS- Thisinvention relates to wayside communication systems for moving trains inwhich an inductive coupling is established between the wayside and trainfor conveying information therebetween. More particularly the inventionrelates to such wayside communication systems of the kind having an openwire transmission line carrying the required information in the form ofelectric currents which produce the magnetic field for the inductivecoupling or which are induced therein by reason of this magnetic field,said open wire transmission line comprising at least one insulatedconductor extending along the track rails and either a further insulatedconductor or a rail of track.

The transmission line in a wayside communication system of this kind isnormally laid at ground level, and when it comprises two insulatedconductors is laid for example on the sleepers and between the rails,the conductors being spaced for example at approximately 30 cm. apart;the conductors are insulated sufficiently to permit free spaceconditions to be assumed under favorable ground conditions.

When ground conditions deteriorate, for example as a result of snow,heavy rain or flooding, free space conditions are no longer assumable;hence increased attenuation is experienced and a variation incharacteristic impedance occurs. These in turn lead to a reduction inthe signal level, which, unless the transmitter operates at asufficiently high power level, can result in a loss of communication.

The object of this invention is to maintain the attenuation andcharacteristic impedance at a substantially constant value under allground conditions.

According to one aspect of the invention, in a wayside communicationsystem of the kind hereinbefore described and having an open wiretransmission line comprising a pair of insulated conductors, eachinsulated conductor has a further electrically conductive memberextending closely adjacent to it and arranged not to interferesubstantially with said inductive coupling, the conductive memberassociated with one insulated conductor being short circuited to theconductive member associated with the other insulated conductor. Theconductive member associated with each of said insulated conductors maycomprise a metal sheathing for the insulated conductor, the sheathing ofat least one of the conductors being in sections insulated from eachother. Both said sheathings may be in sections insulated from each otherand the sections of the sheathing of one conductor are then preferablyeach short circuited with the nearest section of the sheathing of theother conductor.

According to another aspect of the invention, in wayside communicationsystem of the kind hereinbefore described and having an open wiretransmission line comprising an insulated conductor and a rail of thetrack, said insulated conductor has a conductive element extendingclosely adjacent to it and arranged not to interfere substantially withsaid inductive coupling, said conductive member being short circuited tosaid rail.

The invention will now be further explained with reference to theaccompanying diagrammatic drawings, in which:

FIG. 1 is a typical arrangement of wayside conductors,

FIG. 2 is the equivalent circuit thereof,

FIG. 3, 4 and 5 are further equivalent circuits to facilitate theunderstanding of the theoretical considerations of the waysideconductors under certain track conditions, and

FIGS. 6 and 7 are two arrangements of the wayside conductors inaccordance with the invention. FIG. I shows one conventional arrangementof open wire transmission line comprising wayside conductors A and Bspaced 30 cms. apart and laid along the track on the sleepers S, theobject being to produce a vertical electromagnetic field H, at point X,for example 30 cm. above sleeper level. Conversely a field may beradiated from X to induce current in the transmission line. Eachconductor A, B has a central conducting core 1 surrounded by insulation2.

An equivalent circuit of a longitudinal element of the transmission lineassuming free space conditions is shown in FIG. 2; attenuation may becalculated in accordance with normal theory, losses being due to l R,and V /R In practical operating conditions however, ground losses occurand in extreme conditions both conductors may be covered by snow orwater. These conditions can be described, approximately, by theequivalent circuit shown in FIG. 3. The transmission line capacitance C(FIG. I) is no longer that associated with conductor spacing but isdetermined principally by the insulation thickness and permittivityrepresented by capacitance C, and C in FIG. 3; capacitance C can beneglected for the purpose of this description and the equivalent circuitis then given by FIG. 4, or FIG. 5, where capacitance C, in combinationwith leakage conductance G is the parallel equivalent of capacitance C/Z and resistance R When the increased losses due to ground conditionsare significant, the current through resistance R; is determined bycapacitance C /Z since this predominates and is essentially constant.Thus if resistance R (FIG. 4) is made zero, i.e. leakage conductance G(FIG. 5) is zero, the loss due to leakage V 6 is zero.

In FIGS. 6 and 7 are shown two ways in which this effect can be achievedusing a transmission line comprising two insulated conductors A, B. Eachconductor A, B of FIGS. 6, corresponds to conductors A and B of FIG. Iin having a conducting core I and insulation 2. Additionally eachconductor A, B is provided with a thin metal sheath 3 in the manner of acoaxial cable. The metal sheath 3 of each conductor is divided intosections 3, 3" etc. insulated from each other and a sheath section ofone conductor is short circuited to the adjacent sheath section of theother conductor by connections 4. Thus the condition of conductance Gbeing zero is achieved and since the sheath sections are insulated fromeach other the circulation of a screen current is prevented. Therefore,since this arrangement is virtually identical to a transmission line ofthe open wire type, the electromagnetic field at X (FIGQI) isessentially similar. Furthermore the increase in capacitance caused bythe conductive sheaths 3, which are short circuited, reduces thecharacteristic impedance 2,. Thus the power requirement is essentiallylower than that needed for the open wire transmission line shown in FIG.1 and correspondingly, significant savings in terms of transmitting andreceiving equipment is possible.

In FIG. 7 the conductors A", B" again corresponding to conductors A andB in having conducting cores 1 and insulation 2, are provided with ametal sheath but only the sheath 3 of conductor A" is in insulatedsections 3', 3" etc. The conductor B" in this arrangement has acontinuous sheath 3. If desired the conductor B may be used as anindependent coaxial transmission line.

In the case where the open wire transmission line comprises an insulatedconductor and one rail of the track, this will correspond to the FIG. 7arrangement, except that the conductor B" together with its sheath 3will be replaced by one rail of the track.

In a modification of the arrangements of FIGS. 6 and 7, the sheathing ofeach of the conductors can be replaced by an auxiliary conductor wirerunning in the insulation and which is split up into insulated sectionsin like manner to the sheaths in FIG. 6. The auxiliary wire of oneconductor is, as in the case of the metal sheaths described above, shortcircuited with the auxiliary wire of the other conductor. This providesa compromise solution of the same problem.

lclaim:

l. A train-wayside communication system for moving trains wherein aninductive coupling is established between the wayside and train forconveying information therebetween, said system including,

an open wire transmission line extending along the track for carryingsaid information in the form of electric currents which produce amagnetic field for the inductive coupling of said information to saidtrain and alternatively have electric currents induced therein by reasonof a magnetic field for the inductive coupling of said information tothe wayside,

said open wire transmission line comprising a pair of insulatedconductors each having a metal sheathing,

the sheathing of each conductor being in sections insulated from eachother and each section of sheathing of one conductor being shortcircuited to a section of sheathing of the other conductor.

2. A train-wayside communication system for moving trains wherein aninductive coupling is established between the wayside and train forconveying information therebetween,

said system including an open wire transmission line extending along thetrack for carrying said information in the form of electric currentswhich produce a magnetic field for the inductive coupling of saidinformation to said train and alternatively have electric currentsinduced therein by reason of a magnetic field for the inductive couplingof said information to the wayside,

said open wire transmission line comprising an insulated conductortogether with one rail of the track,

said insulated conductor having a metal sheathing which is in sectionsinsulated from each other,

the sections of said sheathing being short circuited to the rail.

1. A train-wayside communication system for moving trains wherein aninductive coupling is established between the wayside and train forconveying information therebetween, said system including, an open wiretransmission line extending along the track for carrying saidinformation in the form of electric currents which produce a magneticfield for the inductive coupling of said information to said train andalternatively have electric currents induced therein by reason of amagnetic field for the inductive coupling of said information to thewayside, said open wire transmission line comprising a pair of insulatedconductors each having a metal sheathing, the sheathing of eachconductor being in sections insulated from each other and each sectionof sheathing of one conductor being short circuited to a section ofsheathing of the other conductor.
 2. A train-wayside communicationsystem for moving trains wherein an inductive coupling is establishedbetween the wayside and train for conveying information therebetween,said system including an open wire transmission line extending along thetrack for carrying said information in the form of electric currentswhich produce a magnetic field for the inductive coupling of saidinformation to said train and alternatively have electric currentsinduced therein by reason of a magnetic field for the inductive couplingof said information to the wayside, said open wire transmission linecomprising an insulated conductor together with one rail of the track,said insulated conductor having a metal sheathing which is in sectionsinsulated from each other, the sections of said sheathing being shortcircuited to the rail.